As data communications traffic in the Internet increases, it is being studied to introduce node apparatuses having a throughput no less than a T bit/s currently, and no less than 10-100 T bit/s in the near future. As means for realizing a node apparatus having such a large transferring capability, an optical router is becoming prevalent since such a capability exceeds the limit of electrical processing. As documents on the optical router, there are a document 1 (K. Shimano et al., in Technical Digest of NFOEC'2001, vol. 1, p. 5, 2001) and a document 2 (K-I Sato et al., “GMPLS-Based Photonic Multilayer Router (Hikari Router) Architecture”, An overview of traffic engineering and signaling technology, IEEE Comm. Mag. vol. 40, pp. 96-101, March 2002), and the like.
As for the optical router, management of an optical communication network is performed in a distributed manner for each node, and optical path connection setting is performed based on signaling processing between the nodes. That is, in an optical communication network using optical routers, setting and management of the optical paths are performed in an autonomous distributed manner for each node.
In the optical communications network, as means for providing highly reliable network services while using resources efficiently, a restoration method is promising. In this method, backup optical path bandwidth accommodated in a route completely different from an active optical path is kept, and the backup optical path bandwidth is shared with a backup optical path for restoring other active optical path. Accordingly, resources of backup optical paths required in a whole network for keeping a certain reliability can be reduced, so that the means is very effective.
In a study of the restoration method by autonomous distributed control (document 3: R. Kawamura et al., “Implementation of self-healing function in ATM networks”, Journal of Network and System Management, vol. 3, no. 3, pp. 243-264, 1995), a principal objective is to implement a self-healing function in an ATM network, in which both an active virtual path (active VP) set in the ATM network and a backup virtual path (backup VP) for restoring the active virtual path are set before a failure occurs. The method of presetting the backup VP defined in the ATM network focuses on setting a route of the backup VP. VP bandwidths in an ATM network can be set successively in units of M Hz. As for the bandwidth of the backup VP, various cases are conceivable such as a case where a same value as the bandwidth of the active VP is ensured or a case where a smaller value than the bandwidth of active VP is ensured. But, as for backup bandwidths that accommodate backup VPs defined for each link, the backup bandwidths are not necessarily set the same as a total sum of bandwidths of active VPs to be restored.
By the way, for implementing the self-healing function by the restoration method based on the autonomous distribution control in a network such as SDH paths and optical paths in which bandwidths are discretely set and bandwidths of an active path need to be completely the same as that of a backup path, it is necessary to extend a signaling protocol for not only setting a route of the backup path but also keeping the bandwidth of the backup path. For example, as shown in FIG. 1, the bandwidth is kept for nodes #1-#3-#6-#8 as an active path. Then, an optical path is created on this route. On the other hand, it is required that bandwidth be only reserved in nodes #1-#2-#4-#7-#8 as a backup path and actual path connection is not performed until the active path becomes unconnectable.
In such a network, a concept of “channel” is important in constructing a management model. An optical network is managed by dividing it into three layers that are an op (optical path) layer, an oms (optical multiplexed section) layer, and an ots (optical transmission section) layer. As for the op layer, the oms layer and the ots layer, an op trail, an oms trail and an ots trail are defined, respectively.
As shown in FIG. 2, an optical channel corresponds to a wavelength bandwidth of an optical region defined between nodes, and corresponds to an op connection that accommodates the oms trail. As for a SDH transmission network, the “channel” corresponds to a VC-3 (50 Mbit/s) or VC-4 (155 Mbit/s) bandwidth defined between cross-connect nodes.
As for backup channels for which backup paths to be used are registered, there are a method for managing the channels in units of one channel, and a method for managing in units of M channels. FIG. 3 shows the method for managing the backup channels in units of one channel. In the method, in the backup optical channels, a backup system for three optical paths (1), (3) and (4) is registered so that 1-to-3 shared backup restoration is realized. The number of backup channels that are actually required is one third of active paths.
In this example, if a failure occurs in the active optical path (1) so that the path is switched to the backup channel, each of active optical paths (3) and (4) enters in a state in which no backup bandwidth is kept in the section. To resolve the state in which failure recovery is not ensured due to such switching, backup path resources are kept again by performing new routing processing, and route change in the backup system occurs. When a failure occurs, there is a possibility that storm of optical path failure recovery requests occur so that network operations may be hindered.
FIG. 4 shows the method for managing the backup channels in units of M channels. A backup channel group consists of two backup channels, and a backup system for five optical paths (1), (3)-(6) is registered so that 2-to-5 shared backup restoration is realized. The number of backup channels actually required is two fifths of actual paths in this example. In this example, even if a failure occurs in the actual optical path (1) and switching to the backup channel occurs, each of other actual optical paths (3)-(6) can be restored by using a remaining one of the backup channels. That is, compared with the method for managing backup channels in units of one channel, it is possible to largely decrease frequency of occurrence of the process for keeping backup path resources again due to failure switching. The method for registering M backup channels for N optical paths is called a M N shared restoration method.
For realizing such networking, a technology for efficiently keeping bandwidths of backup paths is required.
As a design method for accommodating active/backup paths based on the restoration method, there is a method, for example, for estimating the number of wavelengths required for links with respect to traffic demands (optical path demands) in an optical path network based on a wavelength-division multiplexing transmission technology (document 4: K. Nagatsu, “Photonic network design issues and application to the IP backbone”, Journal of Lightwave Technology, vol. 18, no. 12, pp. 2010-2018, December 2000). In the method, when a single link failure occurs, the number of wavelengths necessary for restoring active paths passing through the link is estimated.
A similar technology is also applied to an ATM network in which virtual paths (VP) can be defined on a physical circuit, IP over MPLS in which a label switched path (LSP) can be defined, and Ether over MPLS network. That is, even though the bandwidth that is set for each active virtual path is switched to a backup route by the restoration method at the time when a link failure occurs, the necessary bandwidth set in the virtual path can be kept.
By the way, in actual network operations, there is a case where it is difficult to realize a high-quality communication service only by ensuring failure recovery for a single link failure r1. It is the case where a new different link failure r2 occurs before a path switched to a backup route is reverted to an original active route when recovery of the failed link is completed. At this time, in assignment of resources of backup paths, if a backup path for saving an active path disconnected by the link failure r1 is shared with a backup path for saving an active path disconnected by the link failure r2, there may be a case where the active path disconnected by the link failure r2 cannot be restored, so that a non-operating state of a path may occur.
As mentioned above, in the restoration method, a management control function for autonomously keeping a number of channels or bandwidths required for a channel group accommodating backup paths in units of link becomes important in order to reduce competing states in which a plurality of active paths that switch due to failure in a part of a network apparatus try to keep the same backup path bandwidth with each other.
In addition, in the shared restoration method, it is necessary to recover disconnection of an active optical path due to occurrence of failure of a network for avoiding service interruption as much as possible in the shared restoration method. In addition, as a technology relating to performing failure recovery at high speed, there is a technology disclosed in a document 5 (K. Shimano et al., “Demonstration of Fast Restoration for Distibuted Control Plane on Photonic Network”, Technical Digest in ECOC, lecture number 7.4.2, Copenhagen, September 2002).
For applying the restoration method to a network in which bandwidths of active paths need to be completely the same as bandwidths of backup paths like SDH paths and optical paths and the like, it is necessary to use “pre-assign restoration method” for keeping 100% bandwidth of backup SDH paths or optical paths beforehand. In the pre-assign restoration method, especially, it is required to quickly perform failure switching to a backup path having a long route length.
Further, in a case when multiple failures occur in a network, conflicts for keeping bandwidths may occur in a section in which bandwidth sharing of backup paths is performed so that failure recovery may fail. Therefore, it is required to recover multiple failures as much as possible.
By the way, the document 2 shows a network using optical routers in which a cross-connect technology based on high-reliability switches and a GMPLS (Generalized Multiple Protocol Label Switching) technology for realizing IP network-like distributed control are integrated. As shown in FIG. 5, different from a conventional IP network, the network is configured such that a data plane and a control plane are clearly separated, wherein the data plane is formed by a switch function part for transferring user information of the communication network, and the control plane is formed by a control apparatus for transferring control signals of the communication network. In this configuration, it is required to reduce disconnection of a normal path set in the data plane and unnecessary switching operations as bad influences due to failure of the control plane.